The other day I upgraded a friends computer to Windows 7. Prior doing the upgrade, I had deauthorized her iTunes library to preserve the amount of available authorizations he was allowed. Sometimes upgrading Windows on the same machine can count as another machine. After the upgrade was complete and I was ready to reauthorize the machine, when I launched iTunes, I received the following error message:
The permission error got me curious as this would suggest something related to privilege. I decided to check out what’s going on with this Library.itl file. Here is how I came to resolve this issue.
Click Start > Music
Open the iTunes Library folder
Right click iTunes Library.itl file then click Properties
Go to the Security tab, there was my problem. It seems like during the upgrade, all user permissions were removed for this file. All we need to do is add back all the right groups and users with the correct permissions.
Click Find Now
Select your user account, SYSTEM and the Administrator (Ctrl + Click to select more than one account at time)
Then click OK again
For both users you just added, set the permissions to Full Control
Then click Apply and OK again
You should be able to launch iTunes.